Most studies of European genetic diversity have focused on large-scale variation and
interpretations based on events in prehistory, but migrations and invasions in historical times may also have had profound effects on the genetic landscape. The Iberian peninsula provides a suitable
region to examine the demographic impact of such recent events, since its complex recent history has involved the long-term residence of two very different populations with distinct geographical origins, and their own particular cultural and religious characteristics – North African Muslims, and
Sephardic Jews. To address this question we analysed Y chromosome haplotypes, which provide the necessary phylogeographic resolution, in 1140 males from the Iberian Peninsula and Balearic Islands. Admixture analysis based on binary and Y-STR haplotypes indicates a high mean proportion of ancestry from North African (10.6%) and Sephardic Jewish (19.8%) sources. Despite alternative possible sources for lineages ascribed a Sephardic Jewish origin, these proportions attest to a high level of religious conversion (whether voluntary or enforced), driven by historical episodes of social and religious intolerance, that ultimately led to the integration of descendants. In agreement with the
historical record, analysis of haplotype sharing and diversity within specific haplogroups suggests that the Sephardic Jewish component is the more ancient. The geographical distribution of North African ancestry in the peninsula does not reflect the initial colonization and subsequent withdrawal, and is likely to result from later enforced population movement - more marked in some regions that others – plus the effects of genetic drift.

This is the author's final draft of the paper published as American Journal of Human Genetics, 2008, 83 (6), pp. 725-736. The final version is available from http://www.sciencedirect.com/science/journal/00029297. Doi: 10.1016/j.ajhg.2008.11.007